1. Field of the Invention
The present invention relates to a test arrangement for inspecting the integrity of concrete parts such as, for example the prestressing steel of prestressed concrete construction elements, with a testing head, which has a magnetization device for generating a magnetic field around the construction element, and with a controller for controlling the magnetization process and for processing the signals corresponding with the magnetic field; as well as to a device for such an inspection.
2. The Prior Art
Fractures of the prestressing reinforcement are detected through characteristic anomalies of the magnetic field surrounding the construction element. Such anomalies are based on local variations of the magnetization, or of the magnetic permeability of the prestressing reinforcement. The magnetic field is measured in the course of the magnetization process (measurement in the active field), or after the magnetization process (measurement of the residual field). The problem with the evaluation of the magnetic stray field signals lies in the fact that fracture signals, if any, are superimposed by the signals of the slack reinforcement near the surface.
The test arrangement and the method of magnetic stray field measurement have been employed for some time now for non-invasive inspection of the integrity of the prestressing reinforcement of concrete construction elements. The stray field signals are primarily influenced by the cross girders. Since the construction element is tested from the surface bia a testing head, the spacing of the cross girders from the testing head is smaller than the spacing of the prestressing reinforcement from the testing head. The amplitudes of the girders signals are consequently higher than the emplitudes of the fracture signals--if any--in most cases.
When measuring in the active field, fractures of the pre-stressing reinforcement can be detected by the method of measuring at different magnetization field intensities. Use is made in this connection of the saturation behavior of ferromagnetic materials; the reinforcement near the surface reaches magnetic saturation earlier than the reinforcement located in deeper zones.
Fracture detection thus takes place by this method through the comparison of signals (correlation analysis; weighted signal difference) of measurements that were carried out at different magnetization field intensities. However, the measuring signal still always contains here the signals of the cross girders.
For suppressing the girder signals in residual field measurements, the cross girders are demagnetized with test arrangements and methods of the state of the art by controlling the magnetization process in numerous steps in a manner not described in detail, so that only the signals of a longitudinal reinforcement or prestressing reinforcement will be left. However, it is possible here too that the longitudinal reinforcement is at least partly demagnetized as well, and that possible fracture signals are therefore not detected.